A stone makes a thousand waves.

Three strong bids for electric vehicles formulated by the ministry of industry and information technology were approved and issued by the state administration for market regulation and the standardization administration on May 12, and will come into effect on January 1, 2021.

The three strong standards are GB 18384-2020 "safety requirements for electric vehicles", GB 38032-2020 "safety requirements for electric passenger vehicles" and GB 38031-2020 "safety requirements for power batteries for electric vehicles".

Among the three strong standards, "safety requirements for power batteries for electric vehicles" is the first mandatory standard in the field of power batteries for electric vehicles in China. While optimizing the safety requirements for single batteries and modules, it focuses on strengthening the thermal safety, mechanical safety, electrical safety and functional safety requirements of the battery system.

High-technology lithium electric has noticed that a new test in the standard has attracted the attention of the outside world. In this strong standard, heat diffusion test of the battery system has been added, which requires the battery system to avoid fire and explosion within 5 minutes after a single battery loses control of heat, so as to reserve a safe escape time for passengers.

In this regard, we media have directly issued the argument that "this standard may be the death sentence of ternary power battery", and provided the basis: from the video of the public case, the electric car with ternary lithium battery, from heat out of control to fire and explosion, simply cannot last 5 minutes, tesla, or even only 5 seconds.

For a while, this argument caused the vast majority of the industry to deny that the interpretation is obviously irresponsible, according to the case also clearly confused the definition of the standard.

In this regard, gao gong conducted a survey on the standard's participants, including the makers, leading automobile companies and battery companies, and came to the following conclusions:

From the start of the thermal "alarm signal", the existing mainstream ternary battery can far exceed the standard of five minutes. With the current multi-level protection of cell, module, BMS, PACK, etc., from thermal loss to early warning, and finally to fire, the reserved time is fully sufficient.

To participate in the standard set by the China automobile power battery industry innovation alliance zi-dong wang, deputy secretary-general to introduce high lithium electricity, standard set the bottom line is to build security, life safety for consumers to consider, originally set to 30 minutes, when adjustment was done, 5 minutes is the most basic bottom line requirements. Whatever the system, this standard must be met from a safety standpoint.

As for the definition of the 5-minute time, the standard gives a specific explanation of the test item: after the single battery loses control of heat, the battery system shall not catch fire or explode within 5 minutes and shall not cause danger to the crew cabin. At the same time, a thermal time alarm signal should be provided to allow safe escape time for passengers.

At present, whether the ternary battery can reach the standard of 5 minutes, wang zidong said, it should be not difficult to calculate the time from the loss of heat to the final fire. As for the video case mentioned by we media, it is the time from the smoke to the final fire, rather than the time from the loss of heat to the fire, so it is seriously misleading.

Wang fang, deputy chief engineer of the testing and certification department of China auto center, replied directly on wechat, "the understanding is too superficial."

Gac lithium power then to saic, gac new energy, chang 'an new energy, xiaopeng automobile, ningde times and other car enterprises and battery enterprises to do understanding.

Xiaopeng automobile related personage introduction, from its test of 5 series ternary and high nickel ternary battery system, 5 minutes of the standard can be achieved.

The person in charge of changan new energy said that the non-811 ternary battery system developed by changan can be achieved, and the 811 system has not been tested yet, so there is no data.

Ningde times an insider said that its three - yuan system (including high nickel) battery system can absolutely reach the standard of 5 minutes, and far beyond this level.

Zhu yulong, a senior practitioner, wrote that five minutes is a minimum requirement, and in the long run it takes a longer interval from the runaway heat in a single cell to the fire in a whole package. The ultimate goal is that the cell can get out of control and the car can't burn.

Whether it is automobile companies or battery companies, it has been very clear that the safety precautions of power lithium battery are the most important in three aspects: first, how to design the battery Pack, which includes multiple levels of battery cell, module, BMS and Pack; Second, how to control the heat dissipation of the battery itself; Third, how to design a failure management system to deal with emergencies.

As for the strong target test, we need to focus on the latter two points. Zhu yulong believes that the test raises two core demands:

First, after reaching the standard of out-of-control of cell heat, the battery system USES the sensing system to judge, and then sends an alarm signal that can be perceived by the occupant. This mark serves as a time starting point.

The second is that the battery system cannot threaten the occupant in the first 5 minutes after the starting point (this is actually an experiment with a bag, but measured on the basis of a complete vehicle), and the ultimate meaning is to see if the vehicle catches fire.

In order to achieve these two demands, the current common practice is that through the combination of thermal event parameters: temperature, temperature rise rate, SOC, voltage drop, current, gas concentration, gas pressure, etc., the threshold level of thermal event parameters in the whole process is significantly different from before.

The CNC interpretation is that it depends on the technical solution adopted by the manufacturer and the threshold setting, as well as the hardware system and control, including the sensors used and the signal transmission and control system within the battery system in case of a thermal event.

By means of this method, it is necessary to identify the single cell thermal runaway signal as quickly and effectively as possible after the trigger state.

Next, after identification, thermal runaway countermeasures need to be carried out in an active and passive manner.

The CNC's interpretation is that, in the case of thermal diffusion caused by thermal runaway of a single battery, the battery unit, battery pack or system or vehicle should have the function or characteristic of protecting the occupant.

The main method of active strategy is to exhaust the heat released by a single thermal runaway cell through the thermal management system as soon as possible after the occurrence of thermal runaway in a single cell, so as to make the subsequent transmission of the cell within a single fan as far as possible. Both the nissan Leaf and the audi e-tron have strategies and cases.

The passive strategy is to control the heat loss within a certain range within 5 minutes through insulation and delay. This includes the thermal insulation, flame retardant and high temperature resistance of the material in the PACK to delay the thermal loss; Or add the main control fire control device, not forced to extinguish the fire, but can play the role of preventing combustion and delaying.

Zhu yulong pointed out that the core problem lies in the fact that the process of thermal runaway varies greatly among different chemical systems, cell sizes, cell types, capacity and triggering modes of thermal runaway.

Obviously, the high nickel system is more difficult to control, and the control strategy of different sizes will be different.

"An NCA 5Ah 21700 and a 177Ah NCM811 cell, the whole thermal runaway process is different, and the nearby cells that might be triggered behave differently."

In particular, zhu yulong put forward that the speed of pressure release in the process of thermal runaway of the square shell battery has individual differences. Under certain experimental conditions (high temperature, high SOC), the pressure release exceeds the design of Venting, forming a small explosive zone that can break the local seal. The huge high-temperature gas forms a cutting zone that can explode the local part. If the situation cannot be overcome in 30 seconds, the whole thing will be out of control.

At the macro level, the setting of the strong standard can be interpreted as the control attitude of the safety management organization towards the potential problem of thermal runaway in the future with high energy density.

For high nickel system batteries can meet this standard, high - tech lithium battery is not optimistic.

The policy shows that the bellwether has gone far ahead, and the policy is always ready for the laggards. This for the second and third echelon enterprises of high nickel battery propulsion, may be more difficult to increase.

In the long run, including zhu yulong, a number of people in the industry's view is that the launch of a strong target, for the future development direction is to play a very good role. Policy standards will become increasingly stringent. But yan does not hinder the development of the industry, but to improve consumer confidence, in the long run to help the survival of the fittest industry, so more healthy development.